1. Field of the Invention
The present invention relates to plasma or gaseous discharge display panels and more particularly to detachable circuit modules integral therewith.
2. Description of the Prior Art
Plasma or gaseous discharge display panels such as disclosed, for example, in U.S. Pat. No. 3,499,167 to Baker, et al are well known in the art. Such display panels generally comprise a pair of glass plates mounted in spaced apart relationship forming a sealed chamber, within which is confined a single discharge gas or a mixture of such gases. Each one of the glass plates of the pair comprises on one surface thereof, a pattern of electrodes consisting of separate linear electrical conductors positioned side by side in a parallel relationship to one another. The parallel electrode pattern of one plate is generally, transversely positioned at a 90.degree. angle in relationship to the parallel electrode pattern of the second plate with the electrode surfaces of both plates of the pair facing the internally formed gas chamber. The so combined pair of plates and their associated electrodes forming a grid like array of spaced apart columns and rows of individual electrodes having a plurality of discrete intersecting or cross-point discharge sites.
In the use of such type panels for the display of visual information, selected ones of the cross-point sites are supplied operating discharge and sustaining signals for providing visual light emission at the selected sites. Numerous methods and circuitry for so selecting and addressing the discharge sites have been used in the past and are well known in the art, an example of which is disclosed in U.S. Pat. No. 3,727,102 to Johnson.
It is obvious that a high resolution display panel requires a considerable number of discharge sites and minute spacing between the parallel electrode conductors. One such panel manufactured by Owen-Illinois and identified as Digivue.RTM. Model 512-60, has a resolution of 60 lines or electrodes per inch with a total of 512 individual parallel column electrodes and 512 individual parallel row electrodes. Each alternate electrode of the 512 column electrodes and of the 512 row electrodes extend or exit on opposite ends of their respective glass plates. This provides a reduction of the number of electrode connections per side of the panel and thereby increases the physical spacing therebetween. In this particular example, each one of the four panel sides has 256 conductors to which electrical connections are made between the respective row and column electrodes and the associated selection and addressing circuitry. Typically, each one of these electrical conductors have a width of 0.012 inch and have a spacing, measured from the center of one conductor to the center of the adjacent parallel conductor, of 0.033 inch. In this exemplified display panel there are therefore a total of 1024 relatively narrow and closely spaced electrode conductors to which electrical connections must be made.
In the past, flat and flexible, multiple conductor cables have been used for interconnecting the 1024 panel electrodes with the associated display panel circuitry. The panel ends of the cable conductors are bonded to the display panel conductors by using thermocompression or reflow soldering techniques. Because the conductors on the display panel are generally deposited upon the glass substrate, the bonding operation must be closely controlled to prevent injury to the panel conductors. Both temperature and pressure must be controlled to prevent injury not only to the panel conductors but also to the panel glass substrate as well as to the interconnecting cable and its conductors. The display panel and attached cable assembly result in a somewhat unwieldy package requiring care in handling to prevent injury to the panel, cable, and the bonded connections. An example of this type of prior art is disclosed in U.S. Pat. No. 3,749,959 issued to Schmersal, et al.
The inherent large number of closely spaced and relatively narrow conductors of such display panels require precise control of mechanical alignment of the panel conductors to the respective mating cable conductors prior to and during any conductor bonding operation. This problem exists regardless of whether the bonding is made to the respective conductors of interconnecting cables as described above or to respective conductors of integral circuit modules as herein later described. In addition, irregularities in the glass substrate surface of the display panel or irregularities in the panel electrode conductors themselves, result in un-uniform and uneven pressures to be applied between the panel conductors and the mating interconnecting conductors during the bonding operation, especially when a plurality of such connections are bonded simultaneously. These irregularities also create a problem when nonbonded type connections are made to the display panel such as would be the case with the use of simple type electrical connections which depend solely upon friction and/or pressure for electrical continuity. The build-up of mechanical tolerances in both the panel conductors and the respective mating interconnecting conductors or contacts complicate the problem of making reliable electrical interconnections to the display panel.
In order to reduce the number of discrete interconnecting wire leads to the display panel, the prior art proposes integrally combining the display panel with certain of the selection and addressing circuitry. The combined circuitry is interconnected with the display panel conductors using either conventional solder bonding techniques or simple pressure type contacts as herein previously described. Such prior art is disclosed, for example, in U.S. Pat. Nos. 3,668,688 and 3,684,918 issued to Schmersal.
Although the latter described prior art reduces the number of discrete wire leads to the display panel, and tends to improve the circuit density and packaging of the combined panel and associated circuitry, the problem of the bonding of the electrical interconnections between the display panel electrode conductors and the selection and addressing circuitry still remains. In addition, since certain of the associated circuitry is substantially an integral and permanent part of the display panel, it cannot be easily removed or replaced without possible injury to the display panel or the interconnections between the panel and integral circuitry since the bonded connections must be unbonded and again rebonded for removal and replacement of the circuitry. In addition, repair or replacement of the circuitry integral with the panel cannot be made without the use of special contact bonding and alignment tools. This is, of course, a distinct disadvantage. It is desirable that such integral circuitry be easily and rapidly repaired and replaced both during manufacturing and field maintenance of the display panel and its integral circuitry. The use of circuitry which is an integral part of the display panel and which is not easily removed from the panel also hinders the inclusion of future circuit improvements in already manufactured and existing panels.